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Monday, November 16, 2009

Tacoma Narrows Bridge ( Galloping Gertie)

The Tacoma Narrows Bridge was the first suspension bridge across the Narrows of Puget Sound, connecting the Olympic Peninsula with the mainland of Washington, and a landmark failure in engineering history. Four months after its opening, on the morning of Nov. 7, 1940, in a wind of about 42 miles (68 km) per hour, the 2,800-foot (853-meter) main span went into a series of torsional oscillations the amplitude of which steadily increased until the convolutions tore several suspenders loose, and the span broke up. The bridge was designed to have acceptable horizontal displacement under the static pressure of a much larger wind, but was not designed to handle the dynamic instability caused by an interaction of the winds and the high degree of flexibility of the light, narrow, two-lane bridge. Modeling this type of fluid/structure interaction, a particularly simple type of flutter, was within the technical capability of engineers at the time, but was evidently not considered. A modern analysis would likely view the fluid/structure flutter as a bifurcation problem, and analyze the nature of the bifurcation as the wind speed increased. Immediately after the accident, numerous investigators were able to create both simple mathematical and scale physical models that exhibited the same failure as the actual bridge, and very simple models were able to predict the wind speed that would cause the collapse.

Click on image of bridge to see the spectacular collapse and the sad death of Tubby.*

Design Flaws First Become Apparent

*Note: Tubby, a black male cocker spaniel dog, was the only fatality of the Tacoma Narrows Bridge disaster. Leonard Coatsworth, a Tacoma News Tribune editor, was driving with the dog over the bridge when the bridge started to vibrate violently. Coatsworth was forced to flee his car, leaving Tubby behind. Professor Farquharson and a news photographer attempted to rescue Tubby during a lull, but the dog was too terrified to leave the car and bit one of the rescuers. Tubby died when the bridge fell, and neither his body nor the car were ever recovered. Coatsworth had been driving Tubby back to his daughter, who owned the dog.

Coatsworth received US $364.40 in reimbursement for the contents of his car, including Tubby. In 1975, Coatsworth's wife claimed that Tubby had only three legs and was paralyzed
Poor Tubby.